Building a heat sealer for anti-static bags

[Raphaël Assénat] needed anti-static bags for some boards he is selling. He had a lot of leftovers on hand (presumably from the components he ordered to assemble these boards) and wanted to reuse them. Instead of buying a heat sealer he built his own to cut them down to size.

His build starts with a transformer to drop mains voltage down to 9 Volts. From there, you can see the two power resistors used in series to limit the current. Without these, the wire would get way too hot. Just in front of those resistors is a momentary push switch which cuts the power by default. Here we can see that [Raphaël] is using a wood block to press the bag against the wire as it heats up.

The wire itself is a piece of straightened tension spring. Apparently this spring material is a poor conductor, which is why it gets hot enough to melt the plastic bag when you run current through it.

Using Ohm’s Law (R=V/I in this case), the resistance can be found by dividing the voltage by the current, so the combined value of the resistors AND the hot wire should about 1.8 ohms. I suspect that anyone who wants to make one of these should experiment with various resistor values until they find what works best for their particular setup.
This might just be worth a try…

@atomsoft
from the picture it’s pretty certain it’s 9VAC but DC wouldn’t change the end result by much as if you have current flow,you have heat. The downside of DC I think would be heating of some parts of the circuit more likely.

yeah, I noticed that too. The important thing is that whatever you use doesn’t melt, and doesn’t oxidize excessively (which happens faster at high temperature). In any event, it’s the current that makes the heat. Nichrome wire would probably be ideal. Also, by using nichrome, which has higher resistance than other kinds of wire, you can dump less energy as waste heat in power resistors.

its not the current that makes the heat but the power (I*V) and ideally the resistance of the wire should equal the equivalent resistance of the transformer for most efficient energy transfer (slighly less than 50%)

you of course can buy teflon tape for heat sealers online (no it’s not the same tape you use for water pipes..) – but a cheap source: check for non stick oven liners. it’s cookie baking season, and last year i got a few for $1 after rebate (just don’t get the silicone mats)
and an alternative wire source: the heating wire from an old toaster.

A good conductor will have a low resistance, as P=V^2/R, the larger your resitance in the wire, the more heat will be generated. If you use an ideal wire for example there would be no heat. E.g. Not a very good heat sealer.

So no, you don’t want a good conductor. Although I guess it depends on our definition of good